There's never been an effort in the U.S. House of Representatives to define the term "legitimate rape." But earlier this year, there was an effort to establish "forcible rape" as the one area where federal funds could be used for abortion.

That got a lot of attention but, in terms of actually redefining rape, it had little impact. Republicans tossed out that language in the face of public outcry, and redrafted to cover all rape cases. Even then, the law has sat dormant since May 4, 2011 -- passed by the House but untouched by the Senate.

If you want to know more about how the definition of rape has changed -- and could change in the future -- you'd be better served by looking at what states have done.

They have moved in the opposite direction of House Republicans in recent decades, significantly expanding the legal definitions of rape and giving victims a more expansive set of circumstances that could constitute a sex crime.

As recently as the 1960s, states regularly defined rape as "a carnal knowledgeof a woman not one’s wife by force or against her will." Proving that a rape felony had occurred came with a burden of proof greater than other crimes, such as a robbery or physical assault.

Many states required that women present physical corroboration and immediate reporting as proof that a rape had occurred. For years there were resistance requirements at the state level, where victims had to prove they pushed back against the violation.

"In those theories of practice, there was an expression of skepticism that rape is legitimate," says City University of New York Law School dean Michelle Anderson, who has written extensively on rape law and reform. "To prove it actually happened, you needed to fulfill all those extra burdens."

That began to change in the 1970s, as the feminist movement pushed for more liberal definitions of rape that loosened the traditional reporting requirements. States stopped requiring proof of resistance and corroboration. "Rape shield laws" began to prohibit the introduction of a victim's sexual history into a case, unless it is with the accused.

Michigan became the first state to reform its penal code on rape, with legislation signed in 1975, removing requirements for corroboration and resistance.

"Fully 36 states rape statutes underwent change between 1976 and 1978 alone," Susan Caringella writes in Addressing Rape Reform in Law and Practice. "By the early 1980s, virtually all states had altered their legislation."

Now, only a minority of jurisdictions -- six states and one territory -- now require resistance to prove "forcible rape or sexual assault. Nine jurisdictions, meanwhile, expressly state that no resistance is required.

Researchers at AEquitas, a nonprofit that provides prosecutors with resources on violence against women, recently did a survey looking at rape in the legal system. They saw the "definition of force is broadening beyond overt physical force alone" and "a growing understanding that unwanted and un-consented to bodily invasion is the core wrong that sex crimes must address."

"The research we did saw that the law became more expansive," says AEquitas staff attorney Charlie Whitman. "Over the years, it's become much more expansive to cover different circumstances."

Some changes took longer than others: According to the AEquitas report, it was not until July 1993 that all states allowed the rape or sexual assault of a spouse to be treated as a crime.

While most movement has been at the state level, the federal government has also taken steps to liberalize the definition of rape. The Justice Department announced in January it would broaden the definition of rape it uses in collecting federal statistics on sex crimes. Up until then, the department had used, since 1927, the common law definition of rape as "the carnal knowledge of a female, forcibly and against her will."

The more expansive definition adopted in January acknowledges it as " Penetration, no matter how slight, of the vagina or anus with any body part or object, or oral penetration by a sex organ of another person, without the consent of the victim."

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